Corrupted
by brabbit1029
Summary: Marshall Lee's father, the Ruler of the Nightosphere, arrives declaring that he is going to take over the Land of Aaa. When Marshall Lee sides with his father for unknown reasons, Fionna has no choice but to save the day, even if it means going against someone she really cares about. And along the way, she realizes how little she knows about the mysterious, troubled Vampire King.
1. Prologue

**I do not own Adventure Time, its characters, its plotlines, etc.**

 **I have this recent obsession with Marshall Lee that may soon pass by, but I thought Iight try to squeeze a fanfic out with what I've got. Hope you like it!**

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" _This is how it's supposed to be."_

It was a dark, stormy, and chaotic night. Thick, black clouds ominously crowded the sky, refusing to let a single bit of light shine onto the land below. A strong wind violently whipped past everything, from the thousands of cracks embedded in the earth to the frantic citizens of Aaa running around in fear. The earth trembled beneath their feet, causing some to stumble and trip, only to hurry back onto their feet and continue panicking. From the cracks, skeletons shakily emerged, clumsily making their way onto the ground with rusted swords and other dilapidated weapons in their bony hands. The air was freezing, but people were too busy running for their lives to think about the sub-zero temperature.

" _This is who you are."_

Large holes shone in the air, as if someone had ripped through space itself. Like portals, they revealed a whole different world, one full of fire and atrocious monsters. Demons of all shapes and sizes greedily reached out for the terrified denizens of the other side and grabbed as many of them as they could. The poor citizens were sucked into the holes and mercilessly thrown into the other world. Friends and family were clinging onto each other, struggling to anchor themselves with nearby trees or rocks or anything they could find.

But it was no use. The demonic forces were too strong for them to resist. They could only helplessly run around as monsters destroyed their homeworld and dragged them into an entirely different one.

" _Don't you enjoy it?"_

And in the middle of it all was a single, teenage figure. He wore a long, blood-red cloak with a hood draped over his awfully pale face, concealing his eyes. Strapped to his back was an axe with strings that resembled some sort of guitar. He cackled wildly, as if enjoying the catastrophe, sharp fangs protruding from his mouth as his lips moved up and down. His voice was almost melodic, something ironic given the fact that he was laughing at such disaster. With his hands stuffed into the pockets of his coat, he floated in a nonchalant manner, his skinny legs dangling lazily over the collapsing land.

" _You don't need anyone."_

"Marshall Lee!"

The enigmatic teen's laughter came to an abrupt hault. The smirk on his face still remained as he looked down at the girl below who had called him.

She still wore her signature bunny hat, with a tuft of long blonde hair sticking out and hanging over her face, stained by streaks of dirt brown and blood red. She glared at him with those bright, determined eyes of hers, pleading for him to stop. Her wonderful eyes met his awfully black, red-tinged ones, peeking slightly out from the depths of his hood. She continued to watch him as she hacked away at oncoming monsters with her sword like they were nothing. Behind her, a white and gold cat was backing her up, morphing her body in ways to attack and defend herself. To the side was a male, with skin, hair, and clothes of different shades of pink. He wielded two guns in his hands, blasting away any threats that came nearby.

"Stop this!" The girl demanded as she ran her sword through another demon. "This isn't you!"

" _This IS you!"_

"Marshall!" The pink boy shot a monster before looking up disapprovingly at the floating teen. "Stop this nonsense at once!"

"This isn't funny, paste face!" The shapeshifting cat hollered.

"Paste face" laughed out loud, finding their cries hilarious. Did they think he wasn't doing this on purpose? What a joke! He was evil, a demon. Tainted blood flowed through his very veins. He had the features, the powers, the soul of a monster. He could only destroy. He could bring nothing but pain and fear and suffering.

" _This IS me!"_

His lips curled further into a wicked sneer. A hissing sound escaped from his lips along with a long, forked tongue that wiggled wildly at the people below.

"Marshall!" The girl yelled again. The boy hated that. That stupid, strained voice. Those strong, unwavering eyes. That simple but attractive face, that adorable hat, that stray lock of golden hair that only made her more appealing.

He hated the way it made his insides tingle. He hated how much attention he paid to those details.

He hated it all.

He continued to cackle, as if the situation were all just some big joke. The boy's laughter was light and carefree, yet unhinged, sounding almost insane. He held up one hand, a bolt of lightning streaking through the dark sky along with a loud clap of thunder. More portal-like holes appeared, linking the world to the other dimension-his dimension-his home. Where he truly belonged.

More skeletons rose from underground, and the hordes of monsters screeched in response to his gesture, obeying his every command. For he was the ruler, their leader. He was the vilest of them all.

He was Marshall Lee, the half vampire, half demon, son of the Ruler of the Nightosphere, the Vampire King.

" _I AM a monster."_

He swiftly pulled his arm forward and pointed a clawed finger downwards, signaling his army of demons and the undead to march forward and wreak havoc upon the world. His laughter rang above all the desperate screams, the clangs of weapons against weapons, the cries of despair. The cacophony of horrific sounds were music to his ears.

At least, they were supposed to be.

" _So, why am I…?"_

He lowered his head so that his hood overshadowed his eyes once more. Only his wickedly curved mouth and pointy fangs could be seen, differing greatly from the warm stream of tears that flowed from his concealed demon eyes.

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 **Good? bad? Please let me know!**


	2. Chapter 1

_**Disclaimer: I do not own Adventure Time! And to be honest, I have not watched the entire series, so apologies if I get some stuff wrong. Please correct me if I do!**_

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 _A small, pale boy with a mop of dark hair and matching eyes stood in the middle of pitch black darkness, alone and confused. He frantically looked around for any signs of something, anything, besides the eerie blackness that encaged him._

 _But there was nothing._

" _Hello?" The boy called out. His soft voice, high-pitched due to his young age, echoed across the seemingly endless landscape. Fear coursed through him as he hesitantly walked around, hoping to find an exit of some sort._

 _He tried again. "Hello?"_

" _Marshall."_

 _A kind, familiar voice brought his attention behind him. A tall, thin woman with short, choppy locks of dark hair akin to his stood with an angelic smile that ironically hid her rows of sharp fangs. She wore a simple white dress that somehow made her even more beautiful and stunning. The woman reminded him of warm hugs and the sweet smell of strawberries and vanilla. Relief replaced the frightened expression on his face at the sight of her._

" _Mom!" He dashed towards his mother and held out his arms to embrace her like he always did, but he only grasped thin air and stumbled where she had just been standing. His mother vanished, as if she'd never been there in the first place._

 _He regained his footing and looked around, but his mother was nowhere to be seen. "Mom?! Where are you?!"_

 _He could feel tears beginning to form in his eyes as the grieving sense of loss and longing filled his chest. His mother was gone. His mother was no longer there._

" _She's dead, Marshall."_

 _Another familiar voice caused the boy to freeze. But this time, it wasn't a comforting voice: it was a voice that horrified him and reminded him of dark, awful times. His black eyes grew as wide as saucers as he slowly turned around._

 _A pair of glowing gold eyes with red slits as pupils surrounded by a pale-bluish face caused panic to rise within the boy. The eyes were full of malice and greed, lacking any of the gentleness that his mother's' eyes had._

 _The boy began to tremble. Fearfully, he took a step back. The pale figure continued to glare at him as he grew taller and taller, towering over the cowering boy._

" _She died, Marshall."_

 _The boy cried out as the man reached out a gigantic hand and slammed his massive palm on top of him. The youth found himself falling, as if he'd been thrown into a dark, bottomless pit._

" _You don't need anyone, Marshall."_

" _No!" The boy muttered and shook his head fiercely. He placed his hands over his pointed ears, wanting nothing more than to block that wretched voice out from his world. But it still rang loud and clear in his head. "No! No!"_

" _You're a monster. You don't need anyone."_

 _The boy gasped in horror and brought his hands up to his face. His thin fingers elongated, forming sharp claws. He could feel his body morphing, his feet growing into large gnarly lumps, fur sprouting from his skin. Two thin wings sprouted from his back and flapped wildly behind him as he screamed. His cries came out in high-pitched, nonhuman screeches._

" _Demon. Vampire. Murderer."_

" _No!" The boy sobbed. Crimson red began dripping down the dark scenery as if someone had poured buckets of red paint onto it. A strong hunger throbbed in the boy's gut at the sight of the color, and his mouth began to water._

" _Stop it!" Tears streamed from his now red eyes. He couldn't fight the hunger; it was a monster of its own, gnawing him from the inside out, consuming him. A sweet, savory taste tingled on his taste buds, the taste that the red would provide him if he just took one, little bite..._

" _Don't fight it, Marshall. It's who you are."_

 _The boy helplessly cried and flailed around. But no matter how hard he flapped his wings, he wouldn't stop falling. No matter how hard he tried to block out the voice, he couldn't._

 _He couldn't do anything._

" _Eat, Marshall! Eat!_

" _EAT!"_

" _NO!"_

Marshall Lee abruptly woke up with a gasp, falling from his sleeping position midair onto his bed with a soft thud. The pale vampire panted heavily, still disoriented from his nightmare. The voices still rang clearly in his head as if that wretched man were standing right next to him, hollering in his ear. He swore he could still see blotches of red in the corner of his vision, and the intense sense of falling still coursed through his veins.

"Ugh." Marshall groaned and rubbed his eyes. He sat up and took in some deep breaths in an attempt to calm his rapidly pounding heartbeat.

"That stupid dream again." Marshall frowned and ran a hand through his messy bed hair. Being the Vampire King and the son of a demon, he had plenty of horrors in his life to haunt him. He couldn't forget his past no matter how hard he tried. But lately, his nightmares of his darkest fears had grown even more frequent and disturbing. He wondered his dreams were a warning that something was coming, something bad.

"It couldn't be…" Marshall mumbled. He sighed and heaved himself back into the air. With little effort he soared out of the room and down to the bottom floor of his simple house isolated in a dark, empty cave amid the Land of Aaa. He didn't bother changing out of his wrinkled pajamas: a gray T-shirt with a red no-smoking symbol on the front and blue shorts.

He flew into his kitchen and opened the fridge, revealing a wide assortment of red items: red apples, red berries, red cakes, red lipbalm. He grabbed a shiny apple and sank his fangs into its flawless skin. He made a slurping noise as he sucked the red from the fruit, leaving the apple a dull gray.

"Ah." He breathed out in content. He held the gray apple up in front of him, thinking of the red he had just drained from it and the foreboding red in his nightmare.

"Ugh." He frowned and threw the apple away.

Marshall floated into the living room, leaning back so that he was facing the ceiling, his arms folded behind his head in his usual relaxed position. What should he do today? He could go hang out with Fionna, though he recalled that she and Cake had an important mission from Prince Gumball. He could go to Lump Space Prince's party, but that wouldn't be until later that night. Maybe he could go mess with the goody-two-shoes ruler of the Candy Kingdom himself, something that Marshall often enjoyed.

But the lingering thoughts of his nightmares weighed on his spirits. He tried to assure himself that he was worrying about nothing, but he couldn't help but feel uneasy. What if that man was going to show up? What then? While over the centuries Marshall had grown stronger, he knew he was still no match for _him._ It was highly unlikely that he ever would be.

The nerving anxiousness made Marshall restless, and it irritated him greatly. He scowled. That man always had to ruin his life, even when he wasn't here in person.

Marshall spotted his axe electric guitar sitting the corner of the room and decided to do what he always did when he had something on his mind: play a song.

The familiar feel of the guitar resting perfectly in the nook of his arms somewhat relaxed him. Lyrics formed in his head, reflecting his inner thoughts and emotions. He strummed a few chords on his guitar as the notes to a song naturally came to him. He inhaled once before letting his words flow along with the sounds of his guitar.

" _Oh, I'm small, I'm oh so small_

 _While he stands there, oh so tall_

 _Always haunting my nightmares_

 _Always giving me a scare_

 _Reminding me of the bad,_

 _That always makes me so sad,_

 _That runs through my veins,_

 _That drives me insane_

 _Why am I so helpless,_

 _Why am I so useless,_

 _He's always saying what I can't_

 _Reminding me of what I am_

 _Oh, please, why do you have to stay?_

 _Please just go away._

 _I don't want you here._

 _Please just go away._

Marshall let the last of the song draw out into a long note. His voice slowly faded away along with the sound of his guitar. He felt satisfied like he always did when he poured his heart and soul into a song. This one was especially emotional, since it focused on some of the darkest and most traumatic parts of his long, messed-up life.

The face of the man behind the song's inspiration still mocked him, but he felt slightly better after singing. He found himself hovering over a desk, one of the few pieces of furniture in his house. Marshall wasn't keen on interior decor. He saw no reason to spruce up the place when he was the only one living there.

He opened the drawer of the desk, revealing some papers and guitar strings with a photo on top of it all. Marshall felt a small smile creep onto his lips. He picked up the photo, wrinkled and bent due to age, and stroked the surface of it affectionately with his hand. In the photo, his mother's bright expression was captured eternally, smiling right at him. She had her arms wrapped around the younger, grinning Marshall Lee, resting her cheek affectionately on top of his head. Marshall couldn't recall the last time he'd smiled like that. Those were easier times, a time where he was more innocent and had less worries than he did in the present. Now, his smiles were mischievous and sinister, devoid of any genuine joy or kindness.

He traced the outline of his mother's face with his finger, remembering how wonderful it felt to be hugged by her at the time.

Feeling refreshed and nostalgic, he placed the photo on the desk and continued strumming on his guitar.

He was probably worried about nothing, he assured himself as he played. Nothing bad was going to happen. That man was down in the dark depths of the Nightosphere, having left him alone for many years. He had no reason to show up, since he didn't truly care for Marshall at all.

Nothing was going to happen.

Unfortunately for Marshall Lee, he was very, very wrong.


End file.
